[Repo Assist] feat: add TaskSeq.groupBy, countBy, and partition (195 tests)

release-notes.txt

@@ -5,6 +5,9 @@ Release notes:
     - update engineering to .NET 9/10
     - adds TaskSeq.scan and TaskSeq.scanAsync, #289
     - adds TaskSeq.pairwise, #289
+    - adds TaskSeq.groupBy and TaskSeq.groupByAsync, #289
+    - adds TaskSeq.countBy and TaskSeq.countByAsync, #289
+    - adds TaskSeq.partition and TaskSeq.partitionAsync, #289
 
 0.4.0
     - overhaul all doc comments, add exceptions, improve IDE quick-info experience, #136, #220, #234

src/FSharp.Control.TaskSeq.Test/FSharp.Control.TaskSeq.Test.fsproj

@@ -28,6 +28,7 @@
     <Compile Include="TaskSeq.Fold.Tests.fs" />
     <Compile Include="TaskSeq.Scan.Tests.fs" />
     <Compile Include="TaskSeq.Reduce.Tests.fs" />
+    <Compile Include="TaskSeq.GroupBy.Tests.fs" />
     <Compile Include="TaskSeq.Forall.Tests.fs" />
     <Compile Include="TaskSeq.Head.Tests.fs" />
     <Compile Include="TaskSeq.Indexed.Tests.fs" />

src/FSharp.Control.TaskSeq.Test/TaskSeq.GroupBy.Tests.fs

@@ -0,0 +1,339 @@
+module TaskSeq.Tests.GroupBy
+
+open Xunit
+open FsUnit.Xunit
+
+open FSharp.Control
+
+//
+// TaskSeq.groupBy
+// TaskSeq.groupByAsync
+// TaskSeq.countBy
+// TaskSeq.countByAsync
+// TaskSeq.partition
+// TaskSeq.partitionAsync
+//
+
+module EmptySeq =
+    [<Fact>]
+    let ``TaskSeq-groupBy with null source raises`` () =
+        assertNullArg <| fun () -> TaskSeq.groupBy id null
+
+        assertNullArg
+        <| fun () -> TaskSeq.groupByAsync (fun x -> Task.fromResult x) null
+
+    [<Fact>]
+    let ``TaskSeq-countBy with null source raises`` () =
+        assertNullArg <| fun () -> TaskSeq.countBy id null
+
+        assertNullArg
+        <| fun () -> TaskSeq.countByAsync (fun x -> Task.fromResult x) null
+
+    [<Fact>]
+    let ``TaskSeq-partition with null source raises`` () =
+        assertNullArg
+        <| fun () -> TaskSeq.partition (fun _ -> true) null
+
+        assertNullArg
+        <| fun () -> TaskSeq.partitionAsync (fun _ -> Task.fromResult true) null
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-groupBy on empty sequence returns empty array`` variant = task {
+        let! result =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.groupBy (fun x -> x % 2)
+
+        result |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-groupByAsync on empty sequence returns empty array`` variant = task {
+        let! result =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.groupByAsync (fun x -> task { return x % 2 })
+
+        result |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-countBy on empty sequence returns empty array`` variant = task {
+        let! result =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.countBy (fun x -> x % 2)
+
+        result |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-countByAsync on empty sequence returns empty array`` variant = task {
+        let! result =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.countByAsync (fun x -> task { return x % 2 })
+
+        result |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-partition on empty sequence returns two empty arrays`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.partition (fun _ -> true)
+
+        trueItems |> should be Empty
+        falseItems |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestEmptyVariants>)>]
+    let ``TaskSeq-partitionAsync on empty sequence returns two empty arrays`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getEmptyVariant variant
+            |> TaskSeq.partitionAsync (fun _ -> Task.fromResult true)
+
+        trueItems |> should be Empty
+        falseItems |> should be Empty
+    }
+
+
+module Immutable =
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-groupBy groups by even/odd`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.groupBy (fun x -> x % 2 = 0)
+
+        // should have exactly two groups
+        result |> Array.length |> should equal 2
+
+        let falseKey, oddItems = result[0] // 1 is first, so 'false' (odd) comes first
+        let trueKey, evenItems = result[1]
+        falseKey |> should equal false
+        trueKey |> should equal true
+        oddItems |> should equal [| 1; 3; 5; 7; 9 |]
+        evenItems |> should equal [| 2; 4; 6; 8; 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-groupByAsync groups by even/odd`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.groupByAsync (fun x -> task { return x % 2 = 0 })
+
+        result |> Array.length |> should equal 2
+
+        let falseKey, oddItems = result[0]
+        let trueKey, evenItems = result[1]
+        falseKey |> should equal false
+        trueKey |> should equal true
+        oddItems |> should equal [| 1; 3; 5; 7; 9 |]
+        evenItems |> should equal [| 2; 4; 6; 8; 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-groupBy with identity projection produces one group per element`` variant = task {
+        let! result = Gen.getSeqImmutable variant |> TaskSeq.groupBy id
+
+        result |> Array.length |> should equal 10
+
+        for key, items in result do
+            items |> should equal [| key |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-groupBy preserves first-occurrence key ordering`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.groupBy (fun x -> x % 3)
+
+        // 1 % 3 = 1 → first key is 1
+        // 2 % 3 = 2 → second key is 2
+        // 3 % 3 = 0 → third key is 0
+        let keys = result |> Array.map fst
+        keys |> should equal [| 1; 2; 0 |]
+
+        let _, group1 = result[0] // remainder 1: 1, 4, 7, 10
+        let _, group2 = result[1] // remainder 2: 2, 5, 8
+        let _, group0 = result[2] // remainder 0: 3, 6, 9
+        group1 |> should equal [| 1; 4; 7; 10 |]
+        group2 |> should equal [| 2; 5; 8 |]
+        group0 |> should equal [| 3; 6; 9 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-groupBy with constant key produces single group`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.groupBy (fun _ -> "same")
+
+        result |> Array.length |> should equal 1
+        let key, items = result[0]
+        key |> should equal "same"
+        items |> should equal [| 1; 2; 3; 4; 5; 6; 7; 8; 9; 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-countBy counts by even/odd`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.countBy (fun x -> x % 2 = 0)
+
+        result |> Array.length |> should equal 2
+
+        let falseKey, oddCount = result[0]
+        let trueKey, evenCount = result[1]
+        falseKey |> should equal false
+        trueKey |> should equal true
+        oddCount |> should equal 5
+        evenCount |> should equal 5
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-countByAsync counts by even/odd`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.countByAsync (fun x -> task { return x % 2 = 0 })
+
+        result |> Array.length |> should equal 2
+
+        let falseKey, oddCount = result[0]
+        let trueKey, evenCount = result[1]
+        falseKey |> should equal false
+        trueKey |> should equal true
+        oddCount |> should equal 5
+        evenCount |> should equal 5
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-countBy preserves first-occurrence key ordering`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.countBy (fun x -> x % 3)
+
+        let keys = result |> Array.map fst
+        keys |> should equal [| 1; 2; 0 |]
+
+        let _, count1 = result[0] // remainder 1: 1, 4, 7, 10 → 4 items
+        let _, count2 = result[1] // remainder 2: 2, 5, 8 → 3 items
+        let _, count0 = result[2] // remainder 0: 3, 6, 9 → 3 items
+        count1 |> should equal 4
+        count2 |> should equal 3
+        count0 |> should equal 3
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-countBy with constant key counts all`` variant = task {
+        let! result =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.countBy (fun _ -> "same")
+
+        result |> should equal [| "same", 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partition splits by even`` variant = task {
+        let! evens, odds =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partition (fun x -> x % 2 = 0)
+
+        evens |> should equal [| 2; 4; 6; 8; 10 |]
+        odds |> should equal [| 1; 3; 5; 7; 9 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partitionAsync splits by even`` variant = task {
+        let! evens, odds =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partitionAsync (fun x -> task { return x % 2 = 0 })
+
+        evens |> should equal [| 2; 4; 6; 8; 10 |]
+        odds |> should equal [| 1; 3; 5; 7; 9 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partition with always-true predicate puts all in first array`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partition (fun _ -> true)
+
+        trueItems
+        |> should equal [| 1; 2; 3; 4; 5; 6; 7; 8; 9; 10 |]
+
+        falseItems |> should be Empty
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partition with always-false predicate puts all in second array`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partition (fun _ -> false)
+
+        trueItems |> should be Empty
+
+        falseItems
+        |> should equal [| 1; 2; 3; 4; 5; 6; 7; 8; 9; 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partition preserves element order within each partition`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partition (fun x -> x <= 5)
+
+        trueItems |> should equal [| 1; 2; 3; 4; 5 |]
+        falseItems |> should equal [| 6; 7; 8; 9; 10 |]
+    }
+
+    [<Theory; ClassData(typeof<TestImmTaskSeq>)>]
+    let ``TaskSeq-partitionAsync preserves element order within each partition`` variant = task {
+        let! trueItems, falseItems =
+            Gen.getSeqImmutable variant
+            |> TaskSeq.partitionAsync (fun x -> task { return x <= 5 })
+
+        trueItems |> should equal [| 1; 2; 3; 4; 5 |]
+        falseItems |> should equal [| 6; 7; 8; 9; 10 |]
+    }
+
+
+module SideEffects =
+    [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
+    let ``TaskSeq-groupBy groups side-effecting sequence`` variant = task {
+        let ts = Gen.getSeqWithSideEffect variant
+
+        let! result = ts |> TaskSeq.groupBy (fun x -> x % 2 = 0)
+
+        result |> Array.length |> should equal 2
+        // re-evaluating yields new side-effects (next 10 items: 11..20)
+        let! result2 = ts |> TaskSeq.groupBy (fun x -> x % 2 = 0)
+        result2 |> Array.length |> should equal 2
+        let _, group2 = result2[0]
+        group2 |> Array.sum |> should equal (11 + 13 + 15 + 17 + 19) // odd items from 11–20
+    }
+
+    [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
+    let ``TaskSeq-countBy counts side-effecting sequence`` variant = task {
+        let ts = Gen.getSeqWithSideEffect variant
+
+        let! result = ts |> TaskSeq.countBy (fun x -> x % 2 = 0)
+
+        // 5 odd, 5 even from 1..10
+        let falseKey, oddCount = result[0]
+        let trueKey, evenCount = result[1]
+        falseKey |> should equal false
+        trueKey |> should equal true
+        oddCount |> should equal 5
+        evenCount |> should equal 5
+    }
+
+    [<Theory; ClassData(typeof<TestSideEffectTaskSeq>)>]
+    let ``TaskSeq-partition splits side-effecting sequence`` variant = task {
+        let ts = Gen.getSeqWithSideEffect variant
+
+        let! evens, odds = ts |> TaskSeq.partition (fun x -> x % 2 = 0)
+
+        evens |> should equal [| 2; 4; 6; 8; 10 |]
+        odds |> should equal [| 1; 3; 5; 7; 9 |]
+
+        // second call picks up side effects
+        let! evens2, odds2 = ts |> TaskSeq.partition (fun x -> x % 2 = 0)
+        evens2 |> should equal [| 12; 14; 16; 18; 20 |]
+        odds2 |> should equal [| 11; 13; 15; 17; 19 |]
+    }

src/FSharp.Control.TaskSeq/TaskSeq.fs

@@ -414,3 +414,14 @@ type TaskSeq private () =
     static member scanAsync folder state source = Internal.scan (AsyncFolderAction folder) state source
     static member reduce folder source = Internal.reduce (FolderAction folder) source
     static member reduceAsync folder source = Internal.reduce (AsyncFolderAction folder) source
+
+    //
+    // groupBy/countBy/partition
+    //
+
+    static member groupBy projection source = Internal.groupBy (ProjectorAction projection) source
+    static member groupByAsync projection source = Internal.groupBy (AsyncProjectorAction projection) source
+    static member countBy projection source = Internal.countBy (ProjectorAction projection) source
+    static member countByAsync projection source = Internal.countBy (AsyncProjectorAction projection) source
+    static member partition predicate source = Internal.partition (Predicate predicate) source
+    static member partitionAsync predicate source = Internal.partition (PredicateAsync predicate) source